In some flat panel displays, a backplate is commonly separated from a faceplate using a spacer structure. In high voltage applications, for example, the backplate and the faceplate are separated by spacer structures having a height of approximately 1-2 millimeters. For purposes of the present application, high voltage refers to an anode to cathode potential greater than 1 kilovolt. In one embodiment, the spacer structure is comprised of several strips or individual wall structures each having a width of about 50 microns. The strips are arranged in parallel horizontal rows with each strip extending across the width of the flat panel display. The spacing of the rows of strips depends upon the strength of the backplate and the faceplate and the strips. Because of this, it is desirable that the strips be extremely strong. The spacer structure must meet a number of intense physical requirements. A detailed description of spacer structures is found in commonly-owned co-pending U.S. patent application Ser. No. 08/683,789 by Spindt et al. entitled "Spacer Structure for Flat Panel Display and Method for Operating Same". The Spindt et al. application was filed Jul. 18, 1996, and is incorporated herein by reference as background material.
In a typical flat panel display, the spacer structure must comply with a long list of characteristics and properties. More specifically, the spacer structure must be strong enough to withstand the atmospheric forces which compress the backplate and faceplate towards each other (In a diagonal 10-inch flat panel display, the spacer structure must be able to withstand as much as a ton of compressing force). Additionally, each of the rows of strips in the spacer structure must be equal in height, so that the rows of strips accurately fit between respective rows of pixels. Furthermore, each of the rows of strips in the spacer structure must be very flat to insure that the spacer structure provides uniform support across the interior surfaces of the backplate and the faceplate. The spacer structure must also have a coefficient of thermal expansion (CTE) which closely matches that of the backplate and faceplate to which the spacer structure is attached (For purposes of the present application, a closely matching CTE means that the CTE of the spacer structure is within approximately 10 percent of the CTE of the faceplate and the backplate to which the spacer structure is attached). The temperature coefficient of resistance (TCR) of the spacer structure must also be low. An acceptable spacer structure must meet all of the above-described physical requirements and must be inexpensive to manufacture with a high yield. Besides the physical requirements set forth above, the conventional spacer structure must also meet several electrical property requirements. Specifically, a spacer structure must have specific resistance and secondary emission characteristics, and have a high resistance to high voltage breakdown.
In conventional prior art spacer structures, an insulating material such as alumina is covered with a coating. In such prior art spacer structures, the insulating material has a very high sheet resistance, while the coating has a lower sheet resistance. Other prior art approaches utilize a spacer structure in which both the insulating material and the overlying coating have a very high sheet resistance.
Thus, due to the large number of stringent physical requirements on the bulk of the spacer structure (i.e., high strength, precise resistivity, low TCR, precise CTE, accurate mechanical dimensions etc.) it is desirable to separate out the additional requirements on the properties of the surface. Hence, a need exists for a spacer structure which meets the above-described physical and electrical property requirements without dramatically complicating and/or increasing the cost of the spacer structure manufacturing process.